But scientists say there is no physiological evidence to suggest that sex before competition is bad. In fact, some studies suggest that pre-sports sex may actually aid athletes by raising their testosterone levels, for example.

It is unclear, however, what psychological effects sex may have on an athlete's performance. Some scientists suggest that abstinence could help some athletes concentrate better.

"There are two possible ways sex before competition could affect performance," said Ian Shrier, a sports medicine specialist at McGill University in Montreal, Canada.

"First, it could make you tired and weak the next day," Shrier said. "This has been disproved.

"The second way is that it could affect your psychological state of mind. This has not been tested," he said.

Power Sports

In 2000 Shrier published an editorial titled "Does Sex the Night Before Competition Decrease Performance?" in the Clinical Journal of Sports Medicine. He wrote that the "long-standing myth that athletes should practice abstinence before important competitions may stem from the theory that sexual frustration leads to increased aggression."

The abstinence tradition is particularly strong in power sports, such as boxing and football, in which aggression is considered a valuable trait.

Some people believe the act of ejaculation draws testosterone, the hormone of both sexual desire and aggression, from the body.

"This is a really wrong idea," said Emmanuele A. Jannini of the University of L'Aquila in Italy. Jannini is a professor of endocrinology, the study of bodily secretions, and has studied effects of sex on athletic performance.